Implement `pbkdf2` on `Keystore`

[MegaRedHand]

Context: #1013

Currently, we only support the Scrypt key derivation function. We want to support pbkdf2 since that one's also mentioned in ERC-2335.

[okekefrancis112]

am I to write the pbkdf from scratch using "elixir" and plug the keystore into it?

[MegaRedHand]

No need. We can add https://hex.pm/packages/pbkdf2_elixir as a dependency for that. Most of the work is calling that here:

lambda_ethereum_consensus/lib/keystore.ex

Lines 66 to 67 in a30602e

	defp derive_key!(%{"function" => "pbkdf2"} = drf, _password) do
	%{"dklen" => _dklen, "salt" => _salt, "c" => _c, "prf" => "hmac-sha256"} = drf

[MegaRedHand]

Hey there, @okekefrancis112 ! We ended up implementing this in #1078. Sorry for the trouble!